1. Field of the Invention
The present invention relates to a composition having lower reactivity containing selected mixtures of hydrated calcium hypochlorite with magnesium sulfate heptahydrate.
2. Brief Description of Art
Hydrated calcium hypochlorite is a strong oxidizer and as such can cause a severe increase in the burning rate of combustible material with which it comes in contact. This oxidation characteristic can cause problems both in the transport and storage of the product. For example, fires involving calcium hypochlorite can be quite vigorous, particularly when combustible material is present, including the product""s packaging material itself (e.g., plastic, cardboard). The blends of hydrated calcium hypochlorite and magnesium sulfate heptahydrate of the invention are not classified as a xe2x80x9cDivision 5.1 Oxidizerxe2x80x9d (i.e. they do not increase the burning rate of combustible material) as measured by an internationally recognized test standard, i.e., the United Nations Protocol: Transport of Dangerous Goods: Manual of Tests and Criteria, Section 34; Classification Procedures, Test Methods, and Criteria relating to Oxidizing Substances of Division 5.1.
Products that are xe2x80x9cDivision 5.1 Oxidizersxe2x80x9d are by definition xe2x80x9cdangerous goodsxe2x80x9d for purposes of transport. The following references have discussed this fire-causing problem and offered solutions to it.
U.S. Pat. No. 3,793,216 (Feb. 19, 1974) (assigned to Pennwalt) teaches adding water in the form of a hydrated inorganic salt to anhydrous calcium hypochlorite (less than 1% water) so that the total resulting water in the blend was from 3 to 13% resulting in a product that xe2x80x9cprovides resistance to exothermic, self-propagating decomposition when contacted by flame, spark, or a contaminating organic substancexe2x80x9d. The test used in this patent to verify this property was an xe2x80x9cignition testxe2x80x9d, which contacts the test sample (from 10 to 500 grams) with a lit match, or a drop of glycerin or 2-propanol. Ignition and self-propagation of burning are indicators of failure. Blends that have a delayed reaction, a less vigorous reaction, or a localized reaction compared to anhydrous calcium hypochlorite were considered to be successful blends. However, this xe2x80x9cignition testxe2x80x9d is not a demanding test. Since no fuel is present the procedure does not test the oxidizing properties, i.e., they could still increase the burning rate of combustible materials. In fact, as will be shown below, many blend products described by this Pennwalt patent pass this ignition test but would still be classified as xe2x80x9cDivision 5.1 Oxidizersxe2x80x9d.
U.S. Pat. No. 4,201,756 (May 6, 1980), (assigned to Olin) teaches the coating of calcium hypochlorite with a plurality of layers of inorganic salts. The first layer must be comprised of salts of Periodic Table Group I alkali metal salts (sodium, potassium, lithium, rubidium, cesium or francium.) The salt must be a chloride, chlorate, nitrate, bromide, bromate, or sulfate. The first layer forms a barrier so that incompatible salts such as basic aluminum sulfate, alkalized magnesium sulfate, and sodium borates may be coated with a second layer on the pre-coated calcium hypochlorite without physical contact with the calcium hypochlorite. See column 17, lines 36 to 54. The layers of salt form a physical barrier, which resists dusting and degradation during handling, and also decreases propensity for ignition and self-sustained decomposition when contacted by a lighted match or incompatible organic materials.
There are many differences between this Olin patent and the present invention. First, the requirement that an inert alkaline salt (such as sodium chloride) be added as a barrier between calcium hypochlorite and a material such as magnesium sulfate heptahydrate is not necessary. Second, the requirement that the final water content of the coated calcium hypochlorite be between 0.5 and 10% is actually counter-productive for reducing the oxidizing behavior of calcium hypochlorite. As such, the mechanism is different from that disclosed in this invention, which involves physically mixing the two substances so that they are in physical contact with each other, and maintaining a water content of at least 17%.
The best indicator of the difference between the two ideas is shown using Example XIV in the Olin patent. The example shows that calcium hypochlorite encapsulated with sodium chloride (approximately 21% by weight) prevented ignition of the material when contacted with a lighted match, i.e., it failed to undergo self-sustained decomposition. Our experiments show that physically blending 21% sodium chloride with calcium hypochlorite actually accelerates burning. As stated above, the mechanism is therefore different.
Accordingly, there is a need in this art to produce a calcium hypochlorite product that is not classified as a Division 5.1 Oxidizer and which has enhanced safety (i.e. diminished fire producing) properties. The present invention provides a solution to that need.
Therefore, one aspect of the present invention is directed to non-Division 5.1 Oxidizer compositions consisting essentially of a blend of hydrated calcium hypochlorite and magnesium sulfate heptahydrate, wherein the water content of the blend is at least about 17% by weight of the blend.
These blends of the present invention are not Division 5.1 Oxidizers and will produce fires of dramatically diminished intensity compared to the above-noted prior art blends. Because the products of the present invention are not classified as Division 5.1 Oxidizers, they are not considered dangerous goods for purposes of transport and thus their transportation costs are lower than the above-noted prior art blends.
Also due to the dramatically reduced intensity of any fire involving the blends (compared to currently marketed calcium hypochlorite dihydrate products) the public good is served by the greatly enhanced safety in the storage and transportation of the product.
The term xe2x80x9cnon-Division 5.1 Oxidizer compositionxe2x80x9d as used in the present specification and claims refers to any blend of calcium hypochlorite hydrate and magnesium sulfate heptahydrate that is not classified as UN Division 5.1 Oxidizer according to standard testing procedures now in effect.
The term xe2x80x9cblendxe2x80x9d is used in the present specification and claims refer to any homogeneous or near homogeneous mixture of the two critical materials. It does not include encapsulated or layered products such as covered in U.S. Pat. No. 4,201,756.
The term xe2x80x9chydratedxe2x80x9d as used in conjunction with calcium hypochlorite products in the present specification and claims refers to any calcium hypochlorite product that has a water content of at least 5% by weight of calcium hypochlorite product. Preferably, the compositions of the present invention consist of commercial xe2x80x9chydratedxe2x80x9d (5.5% to 16% water) calcium hypochlorite, CAS number [7778-54-3] and magnesium sulfate heptahydrate, CAS number [10034-99-8]. These preferred blends do not accelerate burning and are therefore non-oxidizers (as measured by the industry standard oxidizer classification test, i.e., United Nations Protocol Transport of Dangerous Goodsxe2x80x94Oxidizing Substances of Division 5.1).
The composition preferably contains at least about 25% by weight of magnesium sulfate heptahydrate and less than about 75% by weight of hydrated calcium hypochlorite. More preferably, these compositions contain from about 25% to about 40% magnesium sulfate heptahydrate and about 60% to about 75% by weight of hydrated calcium hypochlorite.
Also, the amount of water in the blend should be at least about 17% by weight of the total blend; more preferably, about 18% to about 24% by weight of the blend. The granular magnesium sulfate heptahydrate is physically blended with granular calcium hypochlorite to produce an essentially homogeneous granular mixture. As stated above, the blends are not classified as UN Division 5.1 oxidizers.
The composition may also contain small amounts of other materials as long as the presence of those materials does not cause the resulting blend to be classified as a Division 5.1 Oxidizer.
The amount of water in the blend may be calculated by any standard analytical method for measuring water in chemical blends like these. Our preferred method is thermogravimetric analysis (TGA).
The granular blended products of the present invention are ready for packaging, storage, shipping and use in the purification of water and the like. In some cases, it may be desirable to form tablets and other shaped products from these granular blends. Specifically, the blends are useful as water treatment sanitizers (e.g. in swimming pools and spas), and are especially safer to transport and store than calcium hypochlorite itself.
The present invention is further described in detail by means of the following Examples and Comparisons. All parts and percentages are by weight and all temperatures are degrees Celsius unless explicitly stated otherwise.